COCHLIOBOLUS SATIVUS: VII. NUTRITIONAL CONTROL OF THE PATHOGENICITY OF SOME AUXOTROPHS TO WHEAT SEEDLINGS

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Abstract
The pathogenicity of some strains of Cochliobolus sativus to wheat seedlings was determined. The strains comprised prototrophic and auxotrophic mutants from a common parent, heterokaryons synthesized from auxotrophs, diploids obtained from heterokaryons, and recombinants selected from a diploid.Prototrophic mutants and auxotrophs requiring thiamine, arginine, and pyridoxine were as pathogenic as the parent. Methionineless and lysineless mutants were non-pathogenic. Evidence that the nutritional requirements of the latter mutants directly controlled their pathogenicity was: (1) two methionineless and two lysineless auxotrophs were uniformly non-pathogenic; (2) heterokaryons synthesized from methionineless and lysineless strains and from two methionineless strains were pathogenic; (3) diploids heterozygous for the requirements were pathogenic; (4) prototrophic recombinants from a diploid were pathogenic but auxotrophic ones were non-pathogenic; (5) a prototrophic mutant of a lysineless auxotroph was pathogenic; and (6) the pathogenicity of the auxotrophs was temporarily restored when the appropriate growth requirements were provided as external supplements to the host. The results are discussed.